It has been suggested that chronic interstitial lung disease usually exhibits a component of inflammation and, not infrequently, evidence of immunological involvement. The objectives of this Specialized Center of Research project are to examine the contribution of inflammation and the immune system and in particular the involvement of immune complexes in idiopathic (and other) interstitial pneumonitides. Studies of the mechanisms of pulmonary inflammation will include examination of: a. initiating events, especially those mediated by biologically active fragments of the complement system, b. controlling and modulating processes (immunologic and non-immunologic) which would normally serve to limit the progression of the inflammatory reaction; and, c. reparative re-epithelialization mediated by type II pneumocytes, defects in which may significantly contribute to later fibrosis.